1. Field of the Invention
The present invention relates to wet electronic photograph printers using liquid toner including toner grains dispersed in carrier liquid, and in particular, relates to electronic photograph printers having a print-density-controlling function.
2. Description of the Related Art
Technology associated with print-density control for electronic photograph printers using liquid-toner (hereinafter simply called toner) and commonly known is disclosed, for example, in Patent Document 1.
In the technology disclosed in Patent Document 1, the average density of a toner image formed on the surface of a photosensitive drum with a plurality of photo-sensors with reference to a wide reference density patch to maintain the image density by controlling the development bias of a developer apparatus while comparing the average density with a reference value.
This technology enables automatic setting of an initial value for voltage applied onto an anilox roll (toner supplier roll) used in the developer apparatus. In addition, if the density in the reference density patch is not uniform partly because static-charging devices or optical components deteriorate or are soiled partly in their width direction, the image density can be maintained appropriately because the development bias is set to have the average density.
[Patent Document 1] Japanese Unexamined Patent Application, First Publication No. S59-22060
However, the density of the toner image on the surface of the photosensitive drum differs from the density of an image transferred onto the web. Therefore, the technology disclosed in the aforementioned Patent Document 1 does not ensure accurate density control.
In addition, measurement for the density of the toner image is costly because the number of photo-sensors used for the measurement tends to increase in proportion to the number of divided sections of the toner image in an attempt to minimize the width in each session of measuring the density.